Usually when you start off as Kha'Zix early on in the game you're gonna stick to your jungle until 6 because basically Kha'zix at the early stages isn't very effective in terms of damage (if the enemy is half HP or lower, definitely go in with the help of your teammate.)

Usually during that time you will shine in terms of damage because by then you have your dusk blade and you might wanna focus on ganking the losing lanes and taking an early drake (You can solo at 6)

Usually at this stage your part in the teamfights is to take out their ADC or APC depending on who is more fed, avoid tanks as much as possible and don't stay too long in a fight. Try to utilize your ulti to move in and out of fights with the help of Youmuu's and also remember that if you are unseen, your next basic attack will deal extra damage from your passive and your duskblade which is enormous and almost enough to one shot the adc.